Chemical vapor deposition (CVD) processes, and more particularly, organometallic chemical vapor deposition (OMCVD or MOCVD) processes are commonly employed in the semiconductor, optical, and optoelectronic industries for doping or coating a suituable substrate. These processes essentially involve the depositing of a dopant or a thin metal film on a substrate such as silicon. The deposited films can be sources of doping impurities which are driven into the substrate, or the films themselves can have different electrical or optical properties than the substrate. The properties of the film are based primarily on the conditions involved in the deposition and the chemical identity of the deposited film itself. OMCVD processes are particularly advantageous in that organometallic compounds can be found which have significantly higher vapor pressures at moderate temperatures than the corresponding metals. As a result, these compounds decompose to release the corresponding metals or form compounds thereof at those deposition temperatures normally used in the fabrication of semiconductors and other materials.
Typically, in the semiconductor art, fabrication of III-V semiconductors, e.g., gallium arsenide, occurs through a reaction of a group III organometallic source of the type M(III)R.sub.3, wherein M(III)=Al, In or Ga and R is a lower alkyl, with a group V hydride of general formula M(V)H.sub.3, wherein M(V)=P or As. This process has major disadvantages in that in that the group V hydrides used in the reaction are extremely toxic, and their gaseous nature makes them exceedingly dangerous to transport and handle. Furthermore, large excesses of these toxic hydrides are generally required to successfully produce high quality films. Because of these problems, alternative materials have been sought which can be used successfully to produce high quality Group III/Group V films in a safe and effective manner.
Toxicity associated with group V hydride sources has led to the recent development of hydrocarbon-substituted analogs of the type M(V)R.sub.n H.sub.3-n (wherein n=1 or 2) which can be used more safely in vapor deposition applications such as described above. These compounds, such as described in U.S. Pat. No. 4,734, 514, are primarily directed only to the group V metals arsenic (As) and phosphorus (P), and not to antimony (Sb) compounds. The primary reason for the exclusion of antimony from these analogs is the fact that among the group V congeners, i.e., N, P, As and Sb, a sharp division exists in the chemistry of organometallic compounds between N-, P- and As-containing compounds on the one hand, and Sb-containing compounds on the other. For example, the hydrides NH.sub.3, PH.sub.3 and AsH.sub.3 are quite stable at room temperature, yet SbH.sub.3 (stibine) rapidly decomposes to Sb metal and H.sub.2 at similiar temperatures. Further, the methyl and ethyl group V hydride compounds such as NR.sub.n H.sub.3-n, PR.sub.n H.sub.3-n and AsR.sub.n H.sub.3-n (wherein R=ethyl or methyl and n=1 or 2) are all stable at room temperature, whereas antimony compounds SbEt.sub.n H.sub.3-n and SbMe.sub.n H.sub.3-n (Et=ethyl, Me=methyl and n=1 or 2) all decompose at relatively low temperatures. Consequently, one cannot assume the existence of certain Sb compounds, particularly those of the hydrides, on the basis of the existence of the corresponding N, P, and As compounds. It is clear that if one wishes to employ Sb-containing organometallic compounds in the chemical vapor deposition processes described above, one must first overcome their problems with regard to thermal stability. Although Sb(CH.sub.3).sub.3 is thermally stable and is currently used as an Sb source for narrow bandgap semiconductors comprised of InSb, a thermally stable Sb source having at least one hydrogen atom bound to Sb would be preferable.
An examination of the features of the lower alkyl groups methyl, ethyl, propyl and butyl reveals that they all have a relatively small size and/or the presence of beta-hydrogens. The presence of beta-hydrogen atoms is believed to be responsible for the decomposition of organometallic compounds such as Ga(CH.sub.2 CH.sub.2 CH.sub.2 CH.sub.3).sub.3, and may also provide a decomposition route in the chemistry of compounds such as As[C(CH.sub.3).sub.3 ]H.sub.2. It further appears that ligands of small size may facilitate disproportionation reactions. These features, either individually or in combination, may well account for the instability of antimony compounds incorporating these groups. It is thus highly desirable to use this knowledge to overcome the problems of thermal instability associated with antimony hydrides and develop organometallic antimony compounds which are easy to synthesize, thermally stable, and which can be used safety and effectively as a source or an intermediate in chemical vapor deposition.